Numerous semiconductor processing tools are typically utilized during the fabrication of semiconductor devices. One such common semiconductor processor is a chemical-mechanical polishing (CMP) processor. A chemical-mechanical polishing processor is typically used to polish or planarize the front face or device side of a semiconductor wafer. Numerous polishing steps utilizing the chemical-mechanical polishing system can be implemented during the fabrication or processing of a single wafer.
In an exemplary chemical-mechanical polishing apparatus, a semiconductor wafer is rotated against a rotating polishing pad while an abrasive and chemically reactive solution, also referred to as a slurry, is supplied to the rotating pad. Further details of chemical-mechanical polishing are described in U.S. Pat. No. 5,755,614, incorporated herein by reference.
A number of polishing parameters affect the processing of a semiconductor wafer. Exemplary polishing parameters of a semiconductor wafer include downward pressure upon a semiconductor wafer, rotational speed of a carrier, speed of a polishing pad, flow rate of slurry, and pH of the slurry.
Slurries used for chemical-mechanical polishing may be divided into three categories including silicon polish slurries, oxide polish slurries and metals polish slurries. A silicon polish slurry is designed to polish and planarize bare silicon wafers. The silicon polish slurry can include a proportion of particles in a slurry typically with a range from 1–15 percent by weight.
An oxide polish slurry may be utilized for polishing and planarization of a dielectric layer formed upon a semiconductor wafer. Oxide polish slurries typically have a proportion of particles in the slurry within a range of 1–15 percent by weight. Conductive layers upon a semiconductor wafer may be polished and planarized using chemical-mechanical polishing and a metals polish slurry. A proportion of particles in a metals polish slurry may be within a range of 1–5 percent by weight.
It has been observed that slurries can undergo chemical changes during polishing processes. Such changes can include composition and pH, for example. Furthermore, polishing can produce stray particles from the semiconductor wafer, pad material or elsewhere. Polishing may be adversely affected once these by-products reach a sufficient concentration. Thereafter, the slurry is typically removed from the chemical-mechanical polishing processing tool.
It is important to know the status of a slurry being utilized to process semiconductor wafers inasmuch as the performance of a semiconductor processor is greatly impacted by the slurry. Such information can indicate proper times for flushing or draining the currently used slurry.